1. Field of the Invention:
The present invention relates to a mechanical press machine for press forming various kind of components for automobiles and buildings, such as moldings, window sashes and the like.
2. Description of the Prior Art:
Conventionally, when moldings or sashes for automobiles, for example, are produced by press forming operation, an elongate profiled member formed from metal strip or extruded plastic material is cut into the desired length, and then subjected to local cutting, bore formation, bending, drawing or the like, by using a press machine. More particularly, referring to FIGS. 1A to 1D, in order to produce a weather strip belt molding M, for example, which consists of co-extruded thermoplastic polyvinyl chloride resin and stainless steel strip, the co-extruded elongate body is cut into a predetermined length (FIG. 1A). When the elongate profiled body has a relatively complex cross-sectional shape, undesirable deformation of the profiled body tends to occur during the cutting, so that in many cases, it is necessary to effect re-cutting for trimming the cutting edge f of the profiled body. Subsequently, the cutting edge and outer surface portion A are cut away locally (FIG. 1B), and the lower portion B is also cut away locally while the web portion of the profiled body is formed with a square opening C to be connected with a clip or fastener (FIG. 1C). Finally, the end portion D is bent into desired configuration (FIG. 1D). In order to carry out the above-mentioned various press operations in a mass-production factory, it has been a conventional practice to use a plurality of so-called floating press die, with a plurality of press machines arranged along a linearly extending conveyer, requiring a plurality of operating personnels.
Recently, however, in the automobile industry for example, with a great variety of needs of both consumers and manufacturers, a so-called just-on-time manufacturing system (so-called Kanban system) has been widely employed by which unnecessary stocks are to be minimized and a necessary number of required components are promptly produced and delivered to manufacturers whenever necessary. To follow the manufacturer's just-on-time system, for example, all the above-mentioned press operations for producing the molding M should be operated by a single personnel by using one press machine having a plurality of press dies. To make it possible, since the stroke of the press machine, i.e. the distance between the upper and lower dead points of the ram is constant and cannot be changed, an optimum operating condition with respect to a particular press die can be obtained only by adjusting the so-called shut height which is the distance between the upper surface of the bolster of the machine and the lower dead point of the ram. However, the adjustment of the shut height encounters the following problems. Namely, when press dies are secured to the machine and used in trial operation, particularly in case of drawing or bending dies, adjustment of working stroke often becomes necessary by an amount of e.g. 1 to 5 mm. In case of excessive stroke, the adjustment is carried out by grinding the bottom surface of the die, whereas, in case of insufficient stroke, additional plate is inserted between the bolster and the die. On the other hand, when the shut height of the entire machine is adjusted with respect to one particular die only, the shut height for the remaining dies may be inadequate. Furthermore, a slight difference in the bending characteristic cannot be eliminated for each lot of materials, so that the adjustment should be effected with respect to each lot of materials. As shown in FIG. 2, optimum shut height H.sub.1 ', H.sub.2 ', H.sub.3 ', H.sub.4 ', i.e. the distance between the lower dead points and the bolster upper surface for respective dies D.sub.1, D.sub.2, D.sub.3, D.sub.4 are different from each other, so that it is at all impossible, with conventional press machines, to obtain the optimum shut height for each of the dies. The open height positions are shown as H.sub.1, H.sub.2, H.sub.3, H.sub.4 in FIG. 2.